"Your entire UI freezes" doesn't sound right. It's true that anything that accesses the drive will have to wait for it to spin up, but the Spotlight indexer is a background process which the UI shouldn't be waiting for. Is it possible that there is something other than Spotlight which is using the drive?
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Kevin ReidDec 3 '11 at 17:52

@Kevin I agree, it makes no sense. But it isn't limited to any particular app, and frequently occurs when doing something that has nothing to do with the backup drive whatsoever. The drive simply decides at random intervals that it needs to spin up, and whatever I am doing freezes until it completes.
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Adam LassekDec 6 '11 at 1:41

Did you (or anyone else) ever find a solution to this problem?
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HemmOct 16 '14 at 19:02

@Hemm no, I had to resort to ejecting the drive when I wasn't backing up to keep it from freezing my UI. Pretty lame.
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Adam LassekOct 19 '14 at 3:25

You probably should include a command for turning it back on.
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daviesgeekOct 28 '11 at 21:14

mdutil also refuses to turn off Time Machine indexing.
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Adam LassekOct 28 '11 at 21:15

@daviesgeek, good point - I thought it would be reasonably obvious (and was covered in the article)
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JW8Oct 28 '11 at 21:18

You shouldn't turn spotlight off for your main drive unless you know the consequences, such as App Store upgrades will never work again, email searches won't work (if using Apple Mail), etc. Spotlight is a real nuisance but required by the OS for a number of things.
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kakubeiSep 10 '13 at 14:49

DESCRIPTION
The mdutil command is useful for managing the metadata stores for mounted volumes.

The following options are available:
-p Spotlight caches indexes of some network devices locally. This option requests that a local
caches be flushed to the appropriate network device.
-E This flag will cause each local store for the volumes indicated to be erased. The stores will
be rebuilt if appropriate.
-i on | off
Sets the indexing status for the provided volumes to on or off. Note that indexing may be
delayed due to low disk space or other conditions.
-s Display the indexing status of the listed volumes.
-a Apply command to all volumes.
-v Print verbose information when available.